1. Technical Field of the Invention
The present invention relates generally to a rotary electric machine which is equipped with an armature producing torque when subjected to an electromagnetic force and may be used in an automotive engine starter, and more particularly to such a rotary electric machine designed to have a bearing structure with enhanced resistance to thrust load.
2. Background Art
Japanese Patent First Publication No. 11-141443 teaches a starter motor, as illustrated in FIG. 5, which has an armature shaft 100 retained at an end thereof rotatably by a bearing mount 121 formed on an end frame 120 through a bearing 110.
The bearing 110 is implemented by a plain bearing (also called sleeve bearing) and press-fit within the bearing mount 121. The armature shaft 100 is placed in contact of a journal surface thereof with an inner surface of the bearing 110. The bearing 110 has a flange 111 extending in a radius direction from an end thereof facing a communator 130. The flange 111 is placed in direct contact with a rear end of the commutator 130 to bear a thrust load transmitted from an armature.
When the armature is pressed backward (i.e., rightward as viewed in the drawing) during cranking of the engine, it may cause the rear end of the commutator to hit the flange 111 of the bearing 110, so that a thrust load acts on the flange 111. The flange 111 is deformed elastically to absorb most of such impact. Long use of the starter motor will, therefore, cause the flange 111 of the bearing 110 to experience a large number of impacts, so that it may suffer from physical damage.